The Brewers left-hander spent the entire campaign on the disabled list with a facet joint injury in his right back and a left elbow UCL sprain and flexor strain and had surgery in August to remove a bone spur from his left elbow.
But Parra, 29, had his best outing of the young season on Friday night when he tossed two perfect innings and struck out four batters.
"Second inning I thought he threw the ball real well," manager Ron Roenicke said. "First inning the command wasn't quite there and then he got going. He threw some great fastballs. He threw a lot of real good split-fingers. It was a good outing."
In the sixth inning, Parra induced a groundout by Yadier Molina, then struck out Matt Carpenter swinging on an 85-mph changeup and caught Skip Schumaker looking at a 93-mph fastball.
In the seventh he struck out pitcher Jake Westbrook looking on a 91-mph fastball, struck out Tyler Greene swinging on a changeup and got Jon Jay to fly out to left field.
Parra, who lowered his ERA to 3.27, has now struck out 14 batters and walked three in 11 innings over eight appearances.